Sharif Digital Repository

Because of the importance of gas-solid fluidized beds in chemical industrial plants, many experimental and modeling efforts have been conducted the prediction of their behaviors up to now. Gas bubbles have a pivotal role in the hydrodynamics of bubbling gas-solid fluidized beds; so, fundamental understanding of the bubbling behavior of fluidized beds is required to describe bubble-related phenomena such as solids mixing and segregation, reaction conversion, heat and mass transfer, erosion of heat-transfer tubes and particle entrainment. In this work, the effects of different parameters such as bed aspect ratio, bed width, superficial gas velocity, and particle size distribution on the... 

In the present study a novel phenomenological discrete bubble model (DBM) has been developed for freely bubbling gas-solid fluidized bed simulation. In this model the path of each bubble was tracked through the bed. The model can predict the bubble and emulsion phase dynamic behavior very well. At the first stage the model was developed for a pseudo 2-D gas-solid fluidized bed, and then it was adapted for 3-D beds. The emulsion phase assumed to be as an incompressible fluid and the potential flow assumption has been used to find the velocity flow-field around a single isolated bubble. For a swarm of bubbles the superposition rule has been used to find the velocity vector field. In... 

Asphalt concrete is a composite mixture of three phases; aggregate, bitumen and air void. Stress and strain distributions obtained from macroscopic modeling yield different results due to distinctly different mechanical properties of the above-mentioned phases. In this study a more exact analysis of the stress and strain, were carried out by considering the mixture as a two-phase composite; aggregate and mastic phases. Asphalt concrete was considered a composite material consisted of sand mastic and aggregate. Aggregate and mastic phases were separated and response of the loaded asphalt mixture was investigated. Aggregates finer than 2.36 mm in diameter, filler and bitumen consist the... 

Image processing is very important in several applications. Here we use a rectangular grid for image processing. Other approaches exist in the literature. One new approach is to change the grid from rectangular to hexagonal, due to its various advantages over the latter. Main advantage of the hexagonal structure in image processing is its resemblance with the arrangement of photoreceptors in the human eyes. The change in arrangement amounts to requiring less pixels. There is no inconsistency in pixel connectivity and thus angular resolution is higher in this arrangement. Our goal here is to study lossless compression algorithms for images with hexagonal pixels. First, we consider the... 

This thesis has developed a novel platform for digital dentistry which facilitates the interoperability among different digital components and improves digital workflow in a collaborative environment. The platform is inspired by the cloud manufacturing paradigm for enabling the interoperability and collaboration management and also applies the DICOM standard to improve the integration for the coordination among the different stakeholders for better sharing of their resources while they are geographically distributed. The paper has proposed the application of the PACS concept to include design, implant planning, process planning and production workstations. The paper has conducted a... 

Strain softening after the yield point is a prevalent phenomenon in the stress-strain response of cellular solids, consisting of porosities in micro/macro-meter scale, as well as polymers, consisting of free volumes in sub-nanometer molecular scale. Although the underlying micromechanisms for softening in cellular solids are already known, the molecular origin for softening in polymers is still unknown. In this thesis, the micromechanisms of the softening in both materials are investigated. Then, a hypothesis is raised and evaluated to connect the nano-mechanics of softening in polymers to the micro-mechanics of softening in cellular solids. Experiments of compression test, positron-based... 

Today we live in an era of continuous technology improvement which results in huge changes in different areas of diverse industries. Among the most recent systems for monitoring and quality control which benefits from high speed, are machine vision systems. The output of these systems, are digital images that can be used for monitoring instead of the original products. Unfortunately due to the computational complexity of data extracted from the digital images, traditional methods lose their efficiency. Therefore, in this thesis, a method is proposed to design a model for the monitoring and control of image-based processes, which uses classification methods, that are capable of classifying... 

A broad range of plain carbon steels have ferrite-pearlite microstructures, which are used in many industrial applications due to the good strength and formability provided by the typical combination of ferrite grains and pearlite colonies. The mechanical behavior of ferrite-pearlite steels inherently originates from the configurations of ferrite grains and pearlite colonies, which comprised alternating lamellae of cementite with randomly distributed orientations in a ferrite matrix. In this thesis, three different experimental-numerical approaches were employed to investigate the deformation behavior, damage mechanisms, and formability of the ferrite-pearlite steels. At the first step, two... 

Iris segmentation is an essential step in a medical imaging-based automated diagnosis system. The operation of dividing a digital image into areas with different characteristics and setting objectives is known as image segmentation. The extraction of the iris from unnecessary sections of the image is very important for any biometric device. Eyelid / eyelash obstruction, special reflections, intensity heterogeneity, and an irregular iris border, are considered as noise which affect the iris segmentation process. Focusing on Fuzzy C-Means (FCM) clustering and Grasshopper Optimization Algorithm (GOA), we present a new and efficient method for dividing iris-filled, annoying, and iris limits that... 

Fracture Toughness of Geopolymer Concrete Containing Blast Furnace Slag in Corrosive Environments